Cascade developing mechanism for electrography



May 12, 1970 H. T. HODGES 3,511,214

CASCADE DEVELOPING MECHANISM FOR ELECTROGRAPHY Filed March 13, 1968 2 Sheets-Sheet 1 HOWARD T. HODGES INVENTOR.

ATTORNEYS May 12, 1970 H. T. HODGES CASCADE DEVELOPING MECHANISM FOR ELECTROGRAPHY Filed Marchl3, 1968 2 Sheets-Sheet HOWARD T. HODGES INVENTOR.

ATTORNEYS United States Patent 3,511,214 CASCADE DEVELOPING MECHANISM FOR ELECTROGRAPHY Howard T. Hodges, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Mar. 13, 1968, Ser. No. 712,852 Int. Cl. B05b 5/02 US. Cl. 118-637 6 Claims ABSTRACT OF THE DISCLOSURE A recirculating mechanism for cascade developer having an inclined, stepped surface, mounted for oscillation which, in operation, shakes developer to an elevated cascade position.

BACKGROUND OF THE INVENTION This invention relates to the field of electrography and, more specifically, to cascade developing mechanisms for toning electrostatic images (which term is meant to include any electrostatic charge pattern regardless of method of formation).

In the art of electrography, an electrostatic image is formed on an insulating surface, and that image is developed by contacting it with finely divided toner particles, generally of opposite polarity to the image, giving a toner image defined by the electrostatic image. This image is then utilized, for example, by transferring it to a receiving surface and heating it until fixed. In xerography, one form of electrography, the electrostatic image is formed by imagewise exposing a charged photoconductive layer to actinic radiation, thereby dissipating charge in the areas exposed, leaving an electrostatic image corresponding to the unexposed areas of charge.

One of the methods in common use for developing electrostatic images is described in U.S. Pat. No. 2,618,- 551 issued to L. Walkup on Nov. 18, 1952, commonly called cascade development, in which a combination of toner and much larger carrier particles is poured or cascaded from a cascade feed position over a surface carrying the electrostatic image. The carrier and toner are chosen according to their triboelectric properties to impart a desired polarity of charge to the toner. The mixture of the two materials is commonly called a developer. The carrier also performs the function of transporting the powder in the cascading action. It, therefore, must be of proper size, shape and mass to roll over the charge-carrying surface when that surface is in a cascade position.

In most cascade systems, as the developer rolls over the charge-bearing surface, it tones variations in charge. This effect, known as fringe development, gives a large exposure latitude but a hollow appearance to areas intended to be solid with toner. Certain prior art devices have suggested placing a development electrode close to the surface to be toned to attract the lines of force from the image and cause the solid areas to be toned, see for example, U.S. Pat. No. 2,573,881 issued to L. Walkup et al. on Nov. 6, 1951.

In applying cascade developing to automatic equip ment in which an image-bearing surface is continually moved passed a developing station in a cascade position and developer is continually cascaded across it, it becomes necessary to develop a mechanism for recirculating developer. A commonly used mechanism involves an ordinary bucket conveyor. The developer falls from the charge-bearing surface into a bin in which buckets dip. The buckets carry the developer to the top of the mechanism where the buckets empty either into a hopper or 3,51 1,214 Patented May 12, 1970 directly onto the image-bearing surface. Because the system requires substantial length of travel for the eascading developer, the development station must be quite long in a direction of the moving charge-bearing surface. If a bucket-type recirculating system is added with a substantial bin for collection of developer, other dimensions of the station also become quite substantial. In fact, a cascade developing station may be one of the largest single portions of an electrographic machine.

SUMMARY OF THE INVENTION According to the invention, a more compact recirculating mechanism is provided for cascade systems. The prime feature of the mechanism is a stepped surface which is oscillated to propel developer up an incline. This surface can be inclined at the same angle as the charge-bearing surface, and positioned at very close proximity with it, thereby adding compactness to the system.

At the same time, the stepped surface can be on a plate constructed of conducting material which plate then performs a secondary function as a development electrode.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side view of a development apparatus constructed according to the invention;

FIG. 2 is a perspective view of a portion of the apparatus shown in FIG. 1;

FIG. 3 is a schematic side view of another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to FIG. 1, an electrostatic image-bearing surface 1 is moved through a path, a portion of which is inclined to receive cascade developer. Developer is collected in a reservoir 7 which is inclined toward a feed slot 10 from which developer falls onto a lower portion of a stepped surface 3 of a plate 2. The plate 2 is mounted for oscillation with flexure members 4 and 5 which are connected to a housing 11.

In operation, an oscillating driver '6 oscillates plate 2 back and forth in a direction generally parallel to the plate incline. The surface 3 is shaped to inhibit motion of developer in a downward direction but to allow motion upward. This is accomplished [by ratchet-like steps in the surface 3. With these steps, as the plate 2 is moved by the oscillating driver 6 in a direction generally up the incline, the developer is propelled by the steps in that direction. The steps are shaped to allow this movement. When the plate is moved in the opposite direction, developer motion relative to the surface 3 continues to be up the plate until gravity overcomes this motion. The shape of the steps then inhibits the developer from movement down the plate. If the oscillations are given enough force to propel some of the developer to the next step, the developer will be propelled step-bystep up the plate until it reaches a cascade feed position at the top 12 of the plate from which it spills onto the image-bearing surface 1.

The developer cascades across the surface 1 toning the image and then falls onto a surface 9 inclined toward the reservoir 7 to return developer for reuse.

With this design, a reservoir can be used which feeds developer directly to the recirculation means thereby eliminating a large bin used in prior devices. Similarly, a large portion of the recirculation mechanism is only as thick as the plate 2, and, therefore, can be compactly positioned in a machine.

Although the top 12 of the plate 1 is shown as the feed position for cascade developer, more uniform discharge of cascade developer onto the image bearing surface 1 can be obtained by discharging developer from oscillating plate 2 into a hopper, not shown, which be comes the feed position, from which developer is fed onto surface 1.

As toner is used up in the development process, it must be replenished. This can be done by a large number of toner dispensers well known in the art, for example, a toner dispenser 13 shown schematically in FIG. 1 discharging toner into the reservoir 7.

A simple back-and-forth oscillating movement is not the only motion suitable for operation. Other repetitive motions will work. According to FIG. 3, a drive belt 14 moves eccentric drives 15 and 16 to move the plate 2 through a generally orbitable path. Movement of developer up the incline is primarily effected by the vector of the orbital motion which is parallel to the incline and directed up the incline, but also some of the movement in a direction away from the incline aids in propelling the developer over the apex of the next step.

As shown in FIG. 1, the plate 2 may be positioned parallel to the surface 1 and may be constructed of a conductive material in order to also serve a secondary function as a development electrode. In serving this function, the plate may be insulated from ground, connected to an electrical bias or connected to ground to accomplish a variety of results well known in the art. In FIG. 1, the plate is shown connected to a source 17 of electrical bias.

The invention has been described in its application to a moving flexible, charge-carrying surface which can be moved through a path having a long, straight incline, in which application the invention givesits most striking advantages. However, it can also be used with other shapes of surfaces, for example, cylindrically shaped chargebearing surfaces.

The invention has been descirbed in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. For use in an electrographic developing apparatus of the cascade type, in which cascade developer is cascaded from a cascade feed position onto an electrostatic imagebearing surface, allowed to flow down the image-bearing surface under force of gravity, collected in a reservoir and returned to said cascade feed position for reuse, a mechanism for returning said developer to said cascade feed position comprising:

a member having an inclined surface running from said reservoir to said feed position and shaped to transport developer up said surface in res onse to reciprocating motion of said surface, said member having a portion which is electrically conductive and closely spaced to said image-bearing surface, and

means for imparting reciprocative motion to said surface.

2. For use in an electrographic developing apparatus of the cascade type, in which cascade developer is cas caded from a cascade feed position onto an electrostatic image-bearing surface, allowed to flow down the imagebearing surface under force of gravity, collected in a reservoir and returned to said cascade feed position for reuse, a mechanism for mixing components of said developer and returning said developer to said cascade feed position, said mechanism comprising:

a member having an inclined surface extending from said reservoir to said feed position and shaped (a) to inhibit movement of cascade developer down said surface,

(b) to allow movement of cascade developer up said surface, and

(c) to impart movement to cascade developer in a direction up said surface when said surface is moved in a direction up said incline, and

means for imparting repetitive motion to said inclined surface, at least a portion of said motion having a vector with a direction up said incline and a portion of said motion having a vector in a direction down said incline, so that developer received on said surface in said reservoir is transported to said cascade feed position in a manner providing substantial relative movement between the components of said developer.

3. The mechanism according to claim 2 wherein said inclined surface includes a series of steps, the upper part of each step being steep enough to inhibit movement of developer down said surface and to impart movement to the developer up said surface when said surface is moved in a direction up said incline.

4. The mechanism according to claim 2 wherein said means for imparting motion includes an eccentric drive means coupled to said surface for imparting orbital motion to said surface while maintaining the inclination of said surface.

5. In an electrographic developing apparatus for use in applying toner to a moving electrostatic image-bearing surface of a flexible web, which web is adapted to move through a path, a portion of which path is inclined at an angle suitable for cascade development, a cascade developing mechanism comprising:

developer reservoir means having developer feed means,

an elongated plate mounted for oscillatory movement, inclined at approximately said angle and closely spaced to said moving charge-bearing surface, at least a portion of said plate close to said charge bearing surface being electrically conductive and connectable to a source of electrical potential to serve as a development electrode during application of developer to said image-bearing surface.

an upper surface of said plate being positioned to receive developer from said developer feed means and shaped to inhibit movement of cascade developer down said surface, to allow movement of developer up said surface and to impart movement to cascade developer resting on said surface in a direction up said surface when said plate is oscillated, and

means for oscillating said plate in a direction along said incline to move developer to the top of said plate for discharge onto said surface.

6. Mechanism according to claim 5 wherein said reservoir means includes means for receiving developer after it falls from said image-carrying Web including gravity return means for directing said developer to said means, and

wherein said feed means includes a slot in said gravity return means which allows developer to fall onto the lower portion of said incline plate.

References Cited UNITED STATES PATENTS 218,757 8/1879 Martin. 1,720,131 7/1929 Lemont 198220 2,618,376 11/1952 May. 3,332,328 7/1967 Roth 118637 X 3,367,307 2/1968 Lawes et a1 118--312 X JOHN P. MCINTOSH, Primary Examiner U.S. Cl. X.R. 

